1. Field of the Invention
This invention relates to coke and more particularly refers to a new and improved method for manufacturing an isotropic coke.
2. Description of the Prior Art
The term "isotropic coke" is understood in the following to mean coke, the vectorial physical and chemical properties of which are independent of the direction in space, so that, for example, the thermal expansion coefficient of the coke is the same in all directions. Isotropic coke is especially suitable as a base material, for instance, for manufacturing isotropic carbon and graphite bodies. Such bodies have an advantage over bodies with anisotropic properties for certain applications, particularly where these bodies are part of a support structure.
One isotropic coke is Gilsonite coke which is obtained from natural bitumen but is no longer available in sufficient quantity because the deposits are exhausted. According to the German Pat. No. 2,025,979, aromatic hydrocarbons may also be suitable for producing an isotropic coke. These aromatic hydrocarbons contain three and more rings, one of which has five links, and similar N-, O- or S-heterocycles, in which at least one hetero atom is situated in the five-ring. The aromatic hydrocarbons are carbonized alone or as a mixture at a temperature between 430.degree. and 550.degree. C. and a pressure of 4 to 16 bar. The coke carbonized at the low temperature is then calcined in known manner. Particularly well suited for this purpose are compounds such as acenaphthylene, acenaphthene, fluorene, fluoranthene, carbazole, diphenylene oxide and the like. However, the use of such compounds would hardly seem feasible for the production of isotropic coke on a large scale because of their low tar content. The separation of the hydrocarbons and heterocycles as raw material for coking, as proposed in the Patent, from coal tar asphalt fractions or coal tar pitch by means of sodium or sodium amide melts is expensive. German Published Non-Prosecuted application No. 2,300,023, proposes to produce isotropic carbon from hydrocarbon distillates, e.g. from coal tar, by treating the distillate with a gas containing elemental oxygen, where the oxygen requirement is at least 31 liters per kg of distillate and the treatment temperature is 250.degree. to 420.degree. C. The pitch-like treatment residue is coked in known manner by heating under inert conditions. This method has its advantages insofar as tar is available in sufficient quantity, but the relatively small coke residue, which is about 30 to 50%, is a disadvantage.